[mythtv-users] Totally OT - but need help wit RAID5 array

[Robin Hill]

On Thu Nov 16, 2006 at 01:02:17PM -0500, James Pifer wrote:

> Yesterday I created a RAID5 array of 3 160 gig disks. Everything seemed
> ok, copied a bunch of data to it, and all seemed to go fine. I needed
> the space where I was previously holding the data so I had to delete
> some of it. I thought I was safe since I now had it on a RAID5 array.
> Not so, during the night one of the disks started going nuts and was
> apparently removed from the array. See log at bottom.
> 
> Here's the really bad part. I found that when I created my array I
> screwed it up, so my RAID5 was only two disks not three:
> 
> mdadm --create --verbose /dev/md0 --level=5 --raid-devices=3 /dev/hdb /dev/hdc dev/hdd
> 
> Notice the missing "/" in front of dev/hdd.
> 
I'm surprised it didn't complain about this.  I thought it required you
to specify "missing" for any missing devices.

> So I restarted the system praying that it would all come up. So far I
> can't get hdb and hdc back up in the array, although they seem to be
> acting normal. Here are some commands and their output:
> 
> [root at storage ~]# mdadm --assemble /dev/md0 /dev/hdb /dev/hdc
> mdadm: /dev/md0 assembled from 1 drive - not enough to start the array.
> 
> Do I have any chance of recovering any of the data on these drives?
> 
> Any help is appreciated. (and tolerance of my OT is definitely
> appreciated)
> 
Okay - the good news is that with just two drives in the array, the
failed drive should be (almost) as up to date as the working drive.
This means the data _should_ be mostly okay.

You can force assembly of the array by using the --force switch.  I'd
recommend then mounting read-only and copying the data off before
recreating the array with all three drives.  If you don't have enough
space, then you can just hot-add the remaining drive and hope that it
rebuilds okay.  You'll then also need to do a fsck afterwards to check
for any corruptions.

HTH,
        Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <myth at robinhill.me.uk>  |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |
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